CN109891318B

CN109891318B - Lithographic apparatus for generating patterns on a photoresist substrate

Info

Publication number: CN109891318B
Application number: CN201780065057.1A
Authority: CN
Inventors: 阿尔乔姆·博里斯金; 劳伦·布朗德
Original assignee: InterDigital CE Patent Holdings SAS
Current assignee: InterDigital CE Patent Holdings SAS
Priority date: 2016-10-21
Filing date: 2017-10-20
Publication date: 2023-09-29
Anticipated expiration: 2037-10-20
Also published as: WO2018073427A1; US20190243233A1; WO2018073427A9; EP3312674A1; EP3529663A1; EP3529663B1; CN109891318A; US10678127B2

Abstract

In one embodiment of the present disclosure, a lithographic apparatus for generating structures on a photoresist substrate is presented, the lithographic apparatus comprising an illumination unit and a photomask. The photomask is remarkable in that it comprises at least one layer of dielectric material and a medium having a refractive index lower than that of said dielectric material, wherein a surface of the at least one layer of dielectric material has at least one abrupt horizontal change forming a step, and wherein at least the base and the sides of the surface with respect to the step and the propagation direction of electromagnetic waves from the illumination unit are in contact with said medium.

Description

Lithographic apparatus for generating patterns on a photoresist substrate

Technical Field

The present disclosure relates to micro-fabrication techniques, and more particularly, to high resolution nano-jet based lithography techniques.

Background

This section is intended to introduce the reader to various aspects of art, which may be related to various aspects of the present invention that are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. It should be understood, therefore, that these statements are to be read in this light, and not as admissions of prior art.

Photolithography is a fabrication technique that enables transfer of a geometric pattern from a photomask to a photoresist substrate (typically a photopolymer substrate) when the photomask is illuminated by an illumination unit (i.e., when the photomask is exposed to an illumination unit). Such techniques/processes are widely used in the semiconductor industry, particularly for the fabrication of integrated circuits.

In order to design more complex and smaller integrated circuits (as they are dedicated to increasingly compact electronic devices such as tablet computers, mobile phones, etc.), the natural trend in the semiconductor industry is to improve lithography/processes in order to be able to transfer geometric patterns on very small scales (i.e. on the nano metric scale).

The resolution of the lithographic process (i.e., the smallest feature of the geometric pattern that can be produced on the photoresist substrate) is determined by the resolution of the photoresist and the optical resolution of the imaging system. The latter is determined by the wavelength (lambda) of the imaging light and the Numerical Aperture (NA) of the projection lens. For a refractive or reflective optical projection unit, it typically does not exceed one wavelength of the incident light in the host medium. Resolution may be increased by decreasing wavelength or increasing numerical aperture. The latter can be used for contact printing (placing the mask in direct contact with the photoresist substrate), however, it leads to mask degradation and should therefore preferably be avoided. In order to improve the resolution, several techniques have been proposed.

For example, chapter 8 entitled "Nanolithography" in the book entitled "micro/nano electro-mechanical systems and advances in manufacturing technology (Advances in Micro/Nano Eletromechanical Systems and Fabrication Technologies)" written by Gunasekaran Venugopal and Sang-Jae Kim describes and compares several techniques for manufacturing integrated circuits that include nano-geometric patterns. Document US2016/0147138 depicts a specific photomask used in a specific lithographic technique (EUVL (standing for extreme ultraviolet lithography)). Another technique for fabricating integrated circuits including nano-geometric patterns is described in the article entitled "nano-scale material patterning and engineering by atomic force microscopy nano-lithography (Nanoscale materials patterning and engineering by atomic force microscopy nanolithography)" by authors x.n.xie, h.j.chung, c.h.sow, and a.t.s.wee.

In order to design more complex nano-geometric patterns on photoresist substrates, the technique described in document US2016/0259253 was proposed based on near field focusing due to surface plasmon phenomenon. This technique enables super resolution levels of a portion of the incident wavelength. However, this technique relies on the use of a multi-layered metal-dielectric mask, which is costly to manufacture and complexity may be unacceptable for certain applications.

Another technique called nanosphere lithography (NSP) technology, described in the article entitled "deep sub-wavelength process for forming highly uniform nanopore and nanopillar arrays (a deep sub-wavelength process for the formation of highly uniform arrays of nanoholes and nanopillars), published in Nanotechnology 18, 2007 by w.wun et al, provides a cost effective solution for fabricating nanostructures with feature sizes below 100 nm. This technique utilizes a nanojet beam generated by a dielectric sphere (see for details the article entitled "photon nanojet (Photonic nanojets)" by author a.heiretz et al). The use of a monolayer of nano (or micro) spheres deposited on top of a photosensitive material (i.e. photoresist) enables highly selective exposure of the photoresist layer. When exposed to UV light, the hot spot size created by the nanojet microspheres is about half a wavelength in the photoresist material. In this way, microstructures with a feature size scale of 100nm can be fabricated. Thus, nanosphere lithography (NSL) is an economical technique for creating a single layer hexagonal close packing or similar pattern of nanoscale features (see, e.g., article entitled "fabrication of nanoposts by nanosphere lithography (Fabrication of nanopillars by nanosphere lithography)" by author Cheung et al in Nanotechnology 2006). Another example of an application of nanosphere lithography is entitled "photon nanojet lens" by Chen Xu et al, authors published in Nanotechnology 27 (2016): design, fabrication, and characterization (Photon nanojet lens: design, fabrication and characterization) "are described in the article.

Even though nanosphere lithography (NSP) technology is cost and throughput efficient, it may suffer from the following drawbacks:

poor reproducibility due to certain difficulties of precise positioning of the microspheres,

manufacturing tolerances due to imperfections in microsphere shape, size and positioning,

limited diversity of microstructure shapes that can be fabricated (currently limited to simple geometries such as circular nanopores, nanorings and nanopillars).

Accordingly, there is a need to provide alternative techniques to nanosphere lithography that can overcome some of these limitations.

Disclosure of Invention

Reference in the specification to "one embodiment," "an example embodiment," means that the described embodiment may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Furthermore, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

In one embodiment of the present disclosure, a lithographic apparatus for generating structures on a photoresist substrate is presented, the lithographic apparatus comprising an illumination unit, a photomask. The photomask is remarkable in that it comprises at least one layer of dielectric material and a medium having a refractive index lower than that of the dielectric material, wherein a surface of the at least one layer of dielectric material has at least one abrupt level change forming a step, and wherein at least the surface is in contact with the medium with respect to a base and sides of the step.

In a variation, a lithographic apparatus for generating structures on a photoresist substrate is presented. The lithographic apparatus includes an illumination unit and a photomask. The photomask may generate a nano-jet near field pattern that directly modifies the photoresist substrate to obtain the structure. The photomask includes at least one layer of dielectric material and a medium having a refractive index lower than the refractive index of the dielectric material. The surface of the at least one layer of dielectric material has at least one abrupt level change forming a step. At least the base and the side of the surface with respect to the step and the direction of the electromagnetic waves from the lighting unit are in contact with the medium. The nano-jet near field pattern is constructive interference of electromagnetic waves from the base and the side of the surface.

In a preferred embodiment, the photomask is notable in that the step is formed by an edge of at least one cavity made in the at least one layer of dielectric material, and the cavity is at least partially filled with the medium.

In a preferred embodiment, the photomask is notable in that the at least one cavity is a via in the at least one layer of dielectric material.

In a preferred embodiment, the photomask is notable in that the at least one cavity belongs to at least one set of at least two cavities.

In a preferred embodiment, the photomask is notable in that the at least one cavity target is cylindrical or conical.

In a preferred embodiment, the photomask is notable in that the step is formed by an edge of at least one recess made in the at least one layer of dielectric material, and the recess is at least partially filled with the medium.

In a preferred embodiment, the photomask is notable in that the height H of the step is such thatWherein lambda is ₁ Is the wavelength of the electromagnetic wave in the dielectric material.

In a preferred embodiment, the photomask is notable in that it further comprises at least one layer forming a substrate (110) adjacent to the layer of dielectric material.

In a preferred embodiment, the photomask is notable in that the dielectric material belongs to the group comprising:

-glass;

-a plastic;

-a polymeric material.

In a preferred embodiment, the lithographic apparatus is remarkable in that it further comprises an optical projection unit for guiding light from the illumination unit.

In a preferred embodiment, the lithographic apparatus is remarkable in that the optical projection unit comprises a set of lenses and/or mirrors.

Thus, in one embodiment of the present disclosure, an optical projection unit similar to that disclosed in the article entitled "photon injection and its application in nanophotonics (Photonic Jet and its Applications in Nano-Photonics)" published under the authors of Frontiers in Optics/Laser Science 2015 as Hooman Mohseni is used.

In another embodiment of the present disclosure, it is proposed to change/replace the new generation lithography entitled "by UV nanoimprinting" by means of a photomask according to the present disclosure: research and development of materials and processes for microelectronic applications (Lithographie de nouvelle generation par nanoimpression assiee par UV: etude et developpement de materiaux et procedes pour I' application microelectronique) "a mask for use in an optical lithography process, as described in the doctor paper. Thus, several embodiments of the present disclosure may be derived from examples described in such doctor papers.

In one embodiment of the present disclosure, the illumination unit may be selected to transmit a particular electromagnetic wavelength, such as ultraviolet light. Such electromagnetic wavelength may be 365nm or 405nm, for example. The former value (i.e., 365 nm) was used for the simulation reported in fig. 39. In principle shorter wavelength values are also possible, influenced by the properties of the mask material (some materials become opaque at these wavelengths).

In one embodiment of the present disclosure, a lithographic apparatus for generating structures (or patterns) on a photoresist substrate is presented. The lithographic apparatus includes an illumination unit and a photomask. The lithographic apparatus is remarkable in that the photomask comprises at least one layer of dielectric material comprising at least partially a first element having a first refractive index value, the first element comprising at least partially a second element having a second refractive index value being larger than the first refractive index value, and in that the second element comprises at least one base surface defined with respect to the direction of arrival of electromagnetic waves from the illumination unit, and in that the at least one base surface comprises at least two opposite edge line segments, the shape of which and the associated base angle between the at least one base surface and the side of the second element (in a perpendicular plane with respect to the at least one base surface) controls the shape of the at least one focused beam.

In a preferred embodiment, the lithographic apparatus is remarkable in that the second element target has a geometry belonging to the group comprising:

-a column;

-a prism;

-a cone shape;

and wherein the geometric shape has an arbitrary cross section.

In a preferred embodiment, the lithographic apparatus is notable in that the geometry is slanted and/or truncated and/or comprises a rounded top surface.

In a preferred embodiment, the lithographic apparatus is remarkable in that the distance between the at least two opposite edge segments has at least λ ₂ Minimum length of/2, wherein lambda ₂ Is the wavelength of the electromagnetic wave in the material of the second element.

In a preferred embodiment, the lithographic apparatus is characterized in that the edge line of the at least one base surface comprises at least two opposite edge line segments, which may be approximated by straight lines or curved convex lines, each line having at least λ ₂ Length of/2, where lambda ₂ Is the wavelength of the electromagnetic wave in the material of the second element.

In a preferred embodiment, the lithographic apparatus is notable in that the dielectric material has a third refractive index value equal to the second refractive index.

In a preferred embodiment, the lithographic apparatus is characterized in that the first element comprises at least a first base surface defined with respect to the direction of arrival of the electromagnetic wave, and a first side surface connected to the at least one layer of dielectric material, and wherein a minimum distance between each edge line segment of an edge of the at least one base surface and the first side surface is equal to at least λ ₁ 2, wherein lambda ₁ Is the wavelength of the electromagnetic wave in the first element.

In a preferred embodiment, the lithographic apparatus is remarkable in that the first element target has a geometry belonging to the group comprising:

-a column;

-a prism;

-a cone shape;

and wherein the geometry of the first element has an arbitrary cross section.

In a preferred embodiment, the lithographic apparatus is remarkable in that the dielectric material belongs to the group comprising:

-glass;

-a plastic;

-a polymeric material.

In a preferred embodiment, the lithographic apparatus is notable in that the first element is a cavity formed in the at least one dielectric layer.

In a preferred embodiment, the lithographic apparatus is notable in that the size and/or shape of the first element also controls the shape of the at least one focused beam.

In a preferred embodiment, the lithographic apparatus is remarkable in that it further comprises an optical projection unit, and that the optical projection unit comprises a set of lenses and/or mirrors.

Drawings

The foregoing and other aspects of the invention will become more apparent from the following detailed description of exemplary embodiments, read in conjunction with the accompanying drawings, in which:

Figure 1 presents a schematic view of a single layer dielectric microsphere based NSP fabrication technique placed on top of a photoresist layer deposited on a substrate and irradiated by UV light from above;

FIG. 2 (a) is a thick photoresist layer (n ₂ Dielectric microsphere on top (n) =1.7 ₁ =1.5, r=500 nm), using 3D-FDTD electromagnetic simulation software, fig. 2 (b) presents the normalized field intensity in the YZ plane when illuminated from above by UV light (λ=365 nm), fig. 2 (c) presents the normalized field intensity distribution along the X and Y axes at z= -100nm, and fig. 2 (D) presents the normalized field intensity distribution along the Z axis;

FIG. 3 presents a schematic view (side view) of the exposure stage of a lithographic fabrication technique, and a photomask comprising nano-jet generating elements according to one embodiment of the present disclosure and placed on top of a photoresist layer on a substrate;

fig. 4 shows a technique in which a sudden change occurs in the level of the surface of the dielectric layer 112, thereby forming a step in the layer. Fig. 4 (a) shows a side view of the dielectric layer 112. Fig. 4 (b) and 4 (c) show top views in the case of steps with straight edge lines (fig. 4 (b)) and curved (fig. 4 (c)) edge lines, respectively;

5 (a) to 5 (c) are schematic diagrams of field intensity distributions in the imaging plane of three exemplary cylindrical cavities, with different cross-sections illuminated by plane waves propagating along the z-axis (i.e. from the plane of the figure);

fig. 6 shows the topology and sign of cavities formed in a layer of dielectric material according to an embodiment of the present disclosure.

Figures 7 (a) to 7 (e) show the effect of the light when the light is transmitted by plane waves (n ₁ ＝1.49，n ₂ =1) forming a nanojet beam from the hollow cylindrical cavity of fig. 6 having a circular cross section upon irradiation;

figures 8 and 9 provide an analysis of the radiation angle of the nanojet beam of figures 7 (a) to 7 (e);

10 (a) and 10 (b) illustrate complex electromagnetic phenomena of at least some embodiments of the present disclosure;

figures 11 (a) to 11 (c) show the beam not being irradiated from below by a plane wave of unit amplitude, according to an embodiment of the present disclosureNear field plot (n) of nanojet beam generated by hollow cylindrical cavity of high height ₁ ＝1.49，n ₂ ＝1)；

Figures 12 (a) to 12 (d) show the unit amplitude E in the XZ plane _y Nanojet light beams (n) generated by hollow cylindrical cavities at different angles of incidence of plane waves ₁ ＝1.49，n ₂ ＝1)；

13 (a) and 13 (b) illustrate the nano-jet beam phenomenon observed for different host media according to embodiments of the present disclosure;

Fig. 14 shows four exemplary cylindrical cavities, each cavity having a different shape of cross-sectional boundaries, i.e.: (a) circular, (b) square, (c) 8-shaped, and (d) rectangular;

fig. 15 (a) to 15 (d) show the respective simulated near field diagrams-top row for each cavity of fig. 14: from the side view, bottom row: view from above;

fig. 16 presents a schematic view and compares a double-layer annular structure of a cavity consisting of a single core hollow cylinder (fig. 16 (a)) and a core filled with a bulk medium according to one embodiment of the present disclosure (fig. 16 (b)). Arrows schematically represent the propagation directions of the nanojet beams originating from different segments of the cavity base edge line;

figures 17 (a) and (b) present the topology and sign of a ring-shaped nano-jet element/assembly according to one embodiment of the present disclosure, which can be used for photomasks in a lithography system;

fig. 18 presents an annular nano-jet element (n ₁ ＝1，n ₂ =1.49): (a) Side view and symbol, (b) having dimension L _z ＝740nm，R ₁ Power density distribution along z-axis of element with =370 nm, w=500 nm, (c, d) xz (y=0) and xy (z=80 nm from top surface);

figure 19 presents a graph represented by λ according to one embodiment of the present disclosure ₀ Near field characteristics, dimension R, of ring-shaped nano-jet element irradiated by plane wave with unit amplitude of 550nm ₁ Refractive index n=370nm, w=500 nm ₁ ＝1，n ₂ =1.49 and variable height: (a) Power density distribution along the z-axis, in the (b-e) xz (y=0) plane, for element height L _z Power density profile=370, 550, 740 and 1100 nm;

figure 20 shows the light distribution of the light beam at different angles of incidence according to one embodiment of the present disclosure ₀ Power density distribution, dimension L, of annular nanojet element irradiated with plane wave of unit amplitude =550 nm _z ＝740nm，R ₁ =370nm, w=500 nm, and refractive index (n ₁ ＝1，n ₂ =1.49): (a) Along the x-axis (y=z=0), (b-e) xz plane for angles of incidence 0 °, 10 °, 20 °, 30 °, respectively;

figure 21 presents a graph represented by λ according to one embodiment of the present disclosure ₀ Different nanojet beams produced by ring element irradiated by plane wave with unit amplitude of 550nm, dimension L _z ＝740nm，R ₁ =370 nm, refractive index (n ₁ ＝1，n ₂ =1.49), and variable loop width: (a) A power density profile along the z-axis, (b) a maximum of power density along the z-axis (curve labeled 190, left axis) and a focal length (curve labeled 191, right axis) relative to the width of the ring, (c-f) a power density profile in the xz-plane for w=250, 500, 750, and 1000 nm;

Figure 22 presents a graph represented by λ according to one embodiment of the present disclosure ₀ Different power density distribution, dimension R, of ring-shaped nano-jet element irradiated by plane wave of unit amplitude of 550nm ₁ ＝370nm，L _z =370 nm, refractive index (n ₁ ＝1，n ₂ =1.49), and variable loop width: (a) Along the z-axis, (b-e) xz-plane for w=125, 250, 370 and 500nm, respectively;

figures 23 (a) - (c) present different normalized power density distributions in the xz plane for annular nanojet elements illuminated by plane waves of unity amplitude, dimensions r1=370 nm, lz=370 nm, w=500 nm, refractive index (n ₁ ＝1，n ₂ =1.49), and variable loop width: (a) Lambda (lambda) ₀ ＝450nm，(b)λ ₀ ＝550nm，(c)λ ₀ ＝650nm；

FIGS. 24 (a) - (c) present annular nanojets illuminated by plane waves of unity amplitude for the same wavelength of FIG. 23Different normalized power density distributions of elements in xz plane, dimension R ₁ ＝370nm，L _z =740nm, w=500 nm, and refractive index (n ₁ ＝1，n ₂ ＝1.49)：(a)λ ₀ ＝450nm，(b)λ ₀ ＝550nm，(c)λ ₀ ＝650nm；

Figure 25 presents (a) the geometry of an annular nanojet element with circular and square rings, (b) represented by λ ₀ Power density profile along z-axis, dimension L, of annular nanojet element with circular and rectangular cross-section illuminated by plane wave of unit amplitude =550 nm _z ＝740nm，R ₁ ＝370nm，L _x ＝L _y ＝2(R ₁ +W), (c, d) the power density distribution of two elements in the xz plane;

figure 26 discloses a contour plot of the power density with respect to the element core radius and height in fixed points (0, 100 nm) near the top surface of the annular element. The element has a fixed width of ring w=500 nm and is illuminated by a plane wave of unit amplitude. Refractive index of medium: (a) n is n ₁ ＝1，n ₂ ＝1.49，(b)n ₁ ＝2.0；

Fig. 27 presents different topologies of an exemplary ring-shaped nano-jet element;

fig. 28 (a) to (d) present a graph represented by λ ₀ Annular nanojet element with core cylinders of different cross-sections illuminated by plane waves of unit amplitude =550 nm (L _z ＝740nm，W＝500nm，n ₁ ＝1，n ₂ =1.49) power density distribution in xz and xy planes: (a) circular: r is R ₁ =370 nm, (b) square: l (L) _x ＝L _y ＝2R ₁ (c) form 8: r is R ₁ Distance d=r between centers =370 nm ₁ (d) rectangular: l (L) _x ＝8R ₁ ，L _y ＝2R ₁ ；

Fig. 29 presents different power density distributions along the z-axis (x=y=0) of the annular nano-jet element with different cross-sections of the core cylinder shown in fig. 28;

FIGS. 30 (a) - (d) present different power density distributions along the xz and yz axes for the annular nano-jet elements having different cross-sections presented in FIG. 27;

fig. 31 presents the use of a nano-jet focusing element according to one embodiment of the present disclosure;

fig. 32 presents two different views of a second element according to one embodiment of the present disclosure;

fig. 33 presents a second element, the base edge line of which comprises (at least) two pairs of opposite edge line segments, which contribute to the generation of (at least) two nanojet beams, according to one embodiment of the disclosure;

fig. 34 presents the intersection of a portion of the device according to the invention with a plane parallel to the propagation direction of the incident electromagnetic wave (and more precisely in this case with normal incidence electromagnetic waves with respect to the bottom of the dielectric layer);

Fig. 35 (a) - (d) present that a portion of the device according to the invention crosses different results parallel to the plane of propagation of the electromagnetic wave (and more precisely, in this case with normal incidence electromagnetic waves with respect to the bottom of the dielectric layer);

fig. 36 presents a schematic view of a nanojet beam produced by a device (or ring-shaped nanojet element) according to one embodiment of the disclosure illuminated by a plane wave of unit amplitude: (a) Incident from below along the z-axis, (b) incident from the left side along the x-axis. Arrows from the first element indicate the nanojet beam. FIG. 36 (c) presents a power density distribution in the xz plane when the device according to one embodiment of the present disclosure (i.e. comprising a ring structure) is illuminated from the left side (along the x-axis);

figures 37 (a) - (c) present some examples of NJ microstructures (top view): (a) a ring shape, (b) a curved band, (c) a grid, (d) regular or periodic grooves;

fig. 38 (a) presents a CAD model of a hollow annular NJ element forming a double layer cylinder (r1=300 nm, r2=700 nm, h=500 nm) in a glass plate (n1=1.5 nm) placed on top of a photoresist layer (n2=1.7), fig. 38 (b) presents a model of a hollow annular NJ element when formed by a plane wave (λ ₀ =365 nm) normalized field intensity in YZ plane when irradiated from above, fig. 38 (c) shows normalized field intensity distribution along X and Y axes at z= -100nm, and fig. 38 (d) shows normalized field intensity distribution along Z axis;

Fig. 39 presents (a) the normalized field intensity in the XZ plane of a ring-shaped NJ microlens illuminated by a plane wave (λ=365 nm) below 20 ° (if defined with respect to the vertical axis), and (b) the normalized field intensity distribution along the X axis at y=0 nm, z= -100nm for two different angles of incidence of the plane wave. The structural parameters are the same as in fig. 38.

FIG. 40 presents an example of a lithographic apparatus according to an embodiment of the present disclosure;

fig. 41 shows a specific embodiment of the present disclosure, according to which the focusing assembly is based on a 2 x 2 planar array of identical hollow cuboid-shaped cavities embedded in a main medium;

fig. 42 shows an alternative embodiment, in which the hollow cuboid-shaped cavity of fig. 41 is replaced by a hollow cylinder oriented along the plane wave propagation direction;

figure 43 shows a further embodiment in which a 2 x 2 array of hollow cylinders is formed at the boundary of the dielectric medium and the free space;

figure 44 provides two additional exemplary embodiments based on a single-period (figure 44 a) and dual-period (figure 44 b) array of hollow cylinders embedded in a main medium.

Detailed Description

Fig. 1 presents a schematic view of an NSP fabrication technique based on single layer dielectric microspheres placed on top of a photoresist layer deposited on a substrate and irradiated from above by UV light.

Fig. 2 (a) is a CAD model of dielectric microspheres (nl=1.5, r=500 nm) on top of a thick photoresist layer (n2=1.7), analyzed using 3D-FDTD electromagnetic simulation software, fig. 2 (b) presents the results when the UV light (λ ₀ =365 nm) the normalized field intensity in the YZ plane when irradiated from above, fig. 2 (c) presents the normalized field intensity distribution along the X and Y axes at z= -100nm, and fig. 2 (d) presents the normalized field intensity distribution along the Z axis. Note that z=0 corresponds to the top surface of the photoresist layer.

Fig. 3 presents a schematic view (side view) of an exposure stage of a lithographic fabrication technique in which a photomask includes nano-jet generating elements according to one embodiment of the present disclosure and is placed on top of a photoresist layer on a substrate.

Indeed, according to one embodiment of the present disclosure, it is proposed to use a photomask (in a lithographic process or system) that includes elements or structures capable of generating nanojet beams as described below. In one embodiment of the present disclosure, these elements or structures correspond to nano-jet based focusing assemblies.

In one embodiment of the present disclosure, a gap exists between the photomask (the nano-jet mask labeled in fig. 3) and the photoresist layer. Furthermore, such gaps are filled with a medium which may be a gas or a liquid. In a variation (not shown), the photomask is in direct contact with the photoresist layer (i.e., no gaps). Thus, the present techniques can be used for both contact printing and proximity printing on a photoresist layer. It should be noted that in the case of proximity printing, a photomask according to the present disclosure should be placed sufficiently close to the photoresist layer, and the maximum or optimal distance will be determined according to the length of the nanojet beam generated by the photomask.

According to one embodiment of the present disclosure, diffraction of planar electromagnetic waves on a dielectric object with a sudden level of change of its surface (also referred to as a step) may result in formation of a condensed beam (so-called nanojet) that occurs near the step and towards a medium with a higher refractive value. The number of beams and the shape of each individual beam can be controlled by variations in the step size and the shape of the step edge line, while the beam radiation angle and field intensity enhancement in each individual beam can be controlled by variations in the refractive index ratio at the boundary of the object near the step and at the step base angle.

Unlike known diffractive lenses whose focusing power is predicted by Fresnel theory, the nanojet beam isLow dispersion(they have no or less wavelength dependence for the same refractive index ratio between the two materials). Furthermore, a nano-jet focusing assembly (or apparatus) according to the present disclosure may produce a plurality ofIndependent and independentThe light beams (of the same or different shape), which is the case for a fresnel diffraction lensIt is impossible. These unique features make nano-jet based focusing assemblies (or devices) according to the present disclosure attractive for lithography.

Indeed, according to one embodiment of the present disclosure, it is proposed to use a photomask composed of a dielectric layer and comprising cavities/steps as described below.

Fig. 4 to 11 allow an understanding of physical phenomena explaining the formation of nano-jet light beams according to the present disclosure.

Fig. 4 illustrates a technique in which abrupt changes occur in the level of the surface of dielectric layer 112, thereby forming steps in the layer. Fig. 4 (a) shows a side view of the dielectric layer 112. Fig. 4 (b) and 4 (c) show top views in the case where the steps have straight (fig. 4 (b)) and curved (fig. 4 (c)) edge lines, respectively.

As shown in fig. 4 (a), the device is illuminated by a plane wave 20 incident on the device from below along the z-axis with its propagation vector perpendicular to the base plane of the dielectric layer 112. As schematically shown by the dashed arrows in fig. 4 (b) and 4 (c), the nano-jet beam 55 originates from the base edge of the step, which includes a horizontal portion 120 and a side portion 121 (which may also be inclined with respect to the z-axis, forming an arbitrary base angle).

The spots marked 22 to 24 represent the corresponding hot spots in the field intensity distribution in the near region formed in the imaging plane 21. The specific field intensity distribution observed in fig. 4 (c) with two hot spots 23, 24 is associated with the shape of the step edge line with two concave segments responsible for forming two independent nanojet beams.

It should be noted that the curvature of the boundary of the cavity is a means for changing the shape, position and field strength enhancement level of the nanojet beam.

Fig. 5 presents a schematic view of the field intensity distribution in the imaging plane 21 for three exemplary cylindrical cavities with different cross-sections. More precisely, fig. 5 (a) shows a cavity 111a having a circular cross section: the dashed arrow schematically shows that the nanojet beam originates from the base edge of the cavity 111 a. The ring 551 indicates a hot spot in the field intensity distribution in the near region formed by the nanojet beams associated with different segments of the circular base edge line.

Fig. 5 (b) shows a non-rotationally symmetrical cavity 111b whose cross section in the xy-plane is in some way triangular, but one of the three sides of the triangle is concave. Such a generally triangular cavity 111b creates three points 552, 553, and 554, one of which (554) is enhanced due to the concave edge.

Fig. 5 (c) shows a cavity, which is any shape with five straight or concave sections. Points 555 through 559 represent hot spots in the near field distribution due to the nanojet beam originating from the base edge of the step, as schematically indicated by the dashed arrows. The specific field distribution observed in fig. 5 (c) with five hot spots is associated with a specific shape of the edge line with five straight or concave segments responsible for forming five independent nanojet beams.

Fig. 6 illustrates an embodiment of the present disclosure, according to which the step formed at the surface of the dielectric material layer is actually an edge of the cavity 111 formed in the dielectric material layer 112. The present disclosure is of course not limited to such embodiments and any abrupt level change at the surface of the dielectric material is sufficient to produce a physical phenomenon, which will be described below. Such a step can be considered as an edge of an infinitely large cavity in practice.

It must be understood that in the case of cavities, the focusing function is not associated with the whole structure, but with the basic segment of the step discontinuity. Other segments of step discontinuity will help to form the same or other nanojet beam that together can form (i) a broad uniform "leaf-like" nanojet beam with infinite steps (fig. 4 b)), or (ii) a dot or ring with any larger cylindrical cavity (fig. 5 (a)), or (iii) any number of differently shaped partial beams created by the curvilinear edges of any shaped cavity (fig. 5 (b) and 5 (c)).

For simplicity, we therefore focus hereinafter on an example of a cavity 111 formed in a layer of dielectric material 112, as shown in fig. 6.

It can be observed that such a cavity is cylindrical, with a cross section of arbitrary shape. Cylindrical cavity is herein and throughout the document referred to as a cavity shaped as a cylinder, i.e. a surface formed by projecting a closed two-dimensional curve along an axis intersecting the plane of the curve. In other words, such a cylinder is not limited to a true cylinder, but encompasses any type of cylinder, in particular but not limited to, for example, a cuboid or a prism.

The cavity may also have a conical shape. The major axis of which may be perpendicular to the surface of the bottom of the cavity or may be inclined. The cavity may also have an imperfect shape due to manufacturing tolerances, and it must be understood that, for example, a cavity that is targeted to be shaped as a cylinder may become a tapered cavity with an S-shaped cross section during manufacturing.

More generally, such cavities are formed as cylinders or cones of arbitrary cross-section, which can be tuned (optimized) to produce a desired near field pattern, i.e. a desired field intensity distribution in the xy-plane (typically orthogonal to the direction of propagation of the incident wave). The pattern may include one or more hot spots having the same (or different) field strength levels.

Asymmetric cavities are also possible. For example, a cavity with a triangular cross-section in the xy-plane will produce three points. One of these three points may be enhanced if the corresponding face is concave, as will be explained in more detail in connection with the drawings.

Fig. 6 gives some symbols which will be used in the document hereinafter. It can be observed that the cavity is immersed in a refractive index n ₁ Medium 1 (labeled 112)) and filled with a material (air, gas, dielectric, polymeric material.) with a refractive index n ₂ Such that n2<n1。

For example, the cavity may have a cylindrical shape, which is filled with a vacuum (n ₂ =1) and embedded in a homogeneous non-dispersive dielectric medium (with an exemplary refractive index n ₁ =1.49) and is illuminated by a plane wave of linear polarization unit amplitude propagating along the positive z-axis direction, E _y =1 (V/m) (symbol see fig. 6).

Fig. 7 shows the formation of a nanojet beam from such a cavity when illuminated by the plane wave. Rather, the figures7 (a) to 7 (e) each correspond to an incident electromagnetic wave of a different wavelength, i.e. lambda ₀ =450, 500, 550, 600 and 650nm, and shows a near field plot in the XZ plane plotted according to the power density characterized by a time-averaged Poynting (Poynting) vector defined as follows:

wherein E is _m Is the amplitude of the E-field, η is the wave impedance in the host medium and n is the host medium refractive index. Note that, according to equation (1), the power density value associated with a unit amplitude planar wave propagating in a dielectric host medium having a refractive index n is equal to In the following, this value is considered as a reference for the definition of the relative field strength enhancement (FIE) achieved using different types of nano-jet elements embedded in the respective host medium:

FIE＝P/P ₀ [a.u.](equation 2)

Where P is the simulated power density characterized by a time-averaged Potentilla vector, P ₀ Is the reference power density of a plane wave of unit amplitude propagating in the same main medium.

As can be observed in fig. 7, the shape of the nanojet beam and its direction remain stable over a wide wavelength range. A detailed analysis of the radiation angle of the nanojet beam is reported in fig. 8 and 9. Fig. 8 shows the definition of z=z for five different wavelengths of fig. 7 ₀ -L _z In the XZ plane at three different planes. Fig. 9 shows the nanojet beam radiation angle calculated based on the position of the maximum in fig. 8 according to the wavelength.

These data extracted from the near field plot show that the nanojet beam radiation angle does not vary by more than 3 ° for a wavelength range from at least 450 to 750 nm. As shown in fig. 8, the major contribution of the angle change comes from the beam tilt above the column (z ₀ =1500 nm, where z ₀ Is relative to the bottom of the cavityThe relative position of the defined imaging planes, i.e. z ₀ ＝z+L _z ) While the beam shape (at z ₀ At 500 nm) remains stable over the entire wavelength range. This behavior is not typical for fresnel type diffraction lenses and therefore needs to be explained in detail.

The origin of the nanojet beam can be explained by a combination of three electromagnetic phenomena that occur near the base edge of the hollow cavity (or more generally near abrupt level changes in the surface of the dielectric material), namely:

diffraction from refractive index step discontinuities associated with the cavity base 120 (or more generally, with lower level surfaces of steps formed in the host medium),

refraction of the diffracted wave at the vertical edge 121 of the cavity (or more generally on the side of the step), and

interference of the refracted wave and the incident plane wave outside the cavity (or more generally in the main medium).

Fig. 10 presents a schematic diagram illustrating these three phenomena. As shown in fig. 7, 8 and 9, we assume that the host medium is an optically transparent non-dispersive dielectric material with refractive index n ₁ =1.49 (e.g. plastic or glass), and the cavity is filled with vacuum or air, n ₂ =1. The incident plane wave arrives from below in the figure.

The key elements of the complex electromagnetic phenomenon shown in fig. 10 (a) and 10 (b) are as follows:

The incident plane wave induces an equal current at the dielectric-air boundary 120 associated with the cavity base (or more generally, by a sudden horizontal change in its surface when reaching a step of refractive index in the bulk medium);

these induced currents are considered Huygens (Huygens) secondary sources 50 to 53;

according to diffraction theory, the spherical wave 54 radiated by the huygens source causes some power leakage towards the "shadow area", i.e. beyond the lateral boundary 121 of the cavity;

when crossing a lateral (vertical) boundary, the wave radiated by the huyghens source undergoes refraction, resulting in a tilting of the refracted wave over an angle according to Snell-cartesian law.

In fig. 10 (b), we can note that outside the cavity, the wavefront coincides with a different huyghen source location along the cavity baseline, resulting in local field enhancement. The planar shape of these fronts demonstrates the creation of a directed beam propagating from outside the cavity.

Finally, outside the cavity, the refracted wave constructively interferes 56, 57 with the plane wave incident from below, producing a nanojet beam 55.

The nanojet beam generation is therefore explained by the phenomenon of low dispersion in its nature, i.e., (i) edge diffraction, (ii) refraction of the wave at the interface of the two dielectrics, and (iii) interference. This explains why the shape of the light beam and its radiation angle remain stable with respect to the wavelength, as shown in fig. 7 (a) to 7 (e).

Furthermore, the nanojet beam radiation angle is defined by Snell's law (Snell law) and is therefore a function of only two parameters:

-the ratio between the refractive indices of the main medium and the cavity material, and

-base angle of cavity. For simplicity, in the above we only consider cavities with a base angle equal to 90 °, thus having a cylindrical shape with vertical edges

Finally, the nanojet beam formation phenomenon is associated with the edges of the cavity (not the full aperture) and occurs in a 2-D vertical plane perpendicular to the cavity cross-section (symbol see fig. 6).

As shown in fig. 10 (b), the major contribution to the planar wave fronts forming the refracted wave outside the cavity comes from huygens sources 50-53 near the side edge 121 of the cavity. Therefore, the refractive angle of the wave radiated to the outside of the cavity is close to the critical angle of the wave incident on the same boundary from the outside (fig. 10 (a)):

θ ₁ ≈θ _TIR (equation 3)

Wherein θ _TIR ＝sin ^-1 (n ₂ /n ₁ ) Is of refractive index n ₁ And n ₂ Is a critical angle of diopters.

Due to refracted waves and planes incident from belowInterference between the waves ultimately produces a nanojet beam 55. Thus, the nanojet beam (and more generally, the generated nanojet near field pattern) is constructive interference of electromagnetic waves from the base 120 and side 121 of the stepped structure. Thus, the radiation angle (θ _B ) Defined by the vector sum of the two waves, as schematically shown in fig. 10 (a). These considerations result in the approximate formulation of the radiation angle of the nanojet beam as follows:

according to equation (4), at refractive index n ₁ ＝1.49(θ _TIR In the case of a primary medium of 41.8 °, the nanojet beam radiation angle should be θ _B 24 deg., slightly greater than that observed in the full wave simulation (see fig. 9). This difference is explained by the assumptions in the qualitative analysis. First, the analysis does not take into account the difference in the amplitudes of the diffracted/refracted wave and the incident plane wave. Second, it does not take into account light rays emitted from the outside by a huygens source located near the cavity edge, which undergo total internal reflection on the cavity side edge. These light rays are totally reflected also contribute to the formation of the nanojet beam. Note that these two effects are related to the phenomenon of total internal reflection and therefore cannot be accurately characterized using the snell/fresnel model. However, these two effects (i) depend on the ratio of the refractive indices of the two media, and (ii) are such that the nanojet radiation angle is reduced. Thus, the actual nanojet radiation angle may be smaller than the nanojet radiation angle predicted by equation (4).

Fig. 10 (a) to 10 (c) show the results of different heights ((a) h=l) _Z ＝370nm、(b)H＝L _Z ＝740nm、(c)H＝L _Z Cylindrical cavity (n) =1100 nm ₁ ＝1.49，n ₂ =1, r=370 nm) of the nano-jet beam generated when irradiated from below by a unit amplitude plane wave. As can be observed, the nano-jet phenomenon is very pronounced for cavity sizes varying from about one wavelength to several wavelengths in the host medium, i.e. 1/2λ ₁ <L _Z <3λ ₁ 。

A minimum height is required to form the planar wavefront edge 60 shown in fig. 10 (b), which produces a nanojet beam. However, the height of the cavity (or the height of the step) should not be too large compared to the length of the nanojet beam, so that it is useful outside the focusing assembly or device.

As shown in fig. 11 (a) to 11 (c), the length of the nanojet beam may vary from a few wavelengths to several wavelengths in the main medium according to the cavity shape and size.

Based on the 2-D ray trace analysis of fig. 10 (b), the main contribution to the formation of the nanojet beam comes from the feed near the cavity side (or the side of the step). The corresponding "effective aperture" responsible for forming the nanojet beam is estimated to be about half the wavelength in the medium inside the cavity (1/2λ ₂ ) Calculated from the side edges within the cavity. For a cavity having an arbitrary shape, the aperture is defined along a line perpendicular to the cavity edge line (S (see fig. 6) in a plane perpendicular to the direction of propagation of the incident wave).

In the 2-D case (which may correspond to any vertical cross section, e.g., in the xz plane), the local field strength enhancement (FIE) achieved due to nano-jet beam forming is a factor of about 2 compared to the incident plane wave (see equation (2)). By modifying the shape of the cavity cross-section, in particular the shape of the cavity edge line S, a larger FIE can be achieved, as will be explained in more detail below.

The nanojet Beam Width (BWHP) at half power may be from about 1/2 lambda ₁ (of the order of diffraction limit) to several wavelengths and depends more on the shape of the cavity.

Fig. 12 (a) to 12 (d) show a hollow cylindrical cavity (n) ₁ ＝1.49，n ₂ ＝1，L _z =740 nm, r=370 nm), nano-jet light beams generated at unit amplitude plane waves of different incident angles in the XZ plane, that is, θ=0° in fig. 12 (a), θ=10° in fig. 12 (b), θ=20° in fig. 12 (c), θ=30° in fig. 12 (d).

The symmetry of the near field pattern in the XY plane (see fig. 12 (a)) demonstrates that the beam shape and radiation angle remain almost unchanged for TE (transverse electron) and TM (transverse magnetic) polarizations of the incident wave.

Further, in the case of oblique incidence, it can be observed in fig. 12 that the beam radiation angle varies corresponding to the incidence angle of the plane wave. The shape and field strength of the beam are enhanced for up to about θ _B The angle of incidence of (c) remains almost unchanged.

Fig. 13 shows the nano-jet beam phenomena observed for different host media, including standard optical plastics and standard or doped glasses. Such nanojet beams consist of light beams having the same physical dimensions (n ₂ ＝1，L _z =740nm, r=370 nm) but embedded in a refractive index n ₁ =1.49 (fig. 13 (a)) and n ₁ A hollow cylindrical cavity in the main medium of =2.0 (fig. 13 (b)).

The understanding of the nano-jet formation phenomenon shown in fig. 4-13 allows for the design of a variety of devices that can be used as focusing components, beam forming components, or more generally, components (or devices) for forming any desired field intensity distribution in the near zone. These components may be used to convert an incident plane wave into one or more individual beams of light, or conversely, to convert an incident beam (regardless of its wavelength) into a localized plane wave, depending on the symmetric path characteristics of the electromagnetic wave.

As explained above in this disclosure, the formation of the nanojet beam is associated with the sides of a step in the dielectric material layer, or with the side edges of the cavity, but not with its full aperture. By optimizing the shape S of the cross-section of the cavity, the shape of the nanojet beam (S) produced by the cavity can be controlled.

Fig. 14 shows four exemplary cylindrical cavities, each having differently shaped cross-sectional boundaries, namely: (a) circular, (b) square, (c) 8-shaped, and (d) rectangular. Dashed arrows schematically illustrate some perpendicular cut planes and directions of the nanojet beams produced when these cavities are illuminated by plane waves propagating along the z-axis from the plane of the figure. These cutting planes are defined with respect to the direction of a normal vector defined at a corresponding point of the cavity cross-section boundary. FIGS. 15 (a) through 15 (d) show corresponding simulated near field diagrams for each cavity, showing the unit amplitude plane propagated in the positive z-axis directionWave irradiation having the same height and radius but different cross-sectional shape (L _z ＝L _x Hollow cavities of =2r=740 nm in xz plane (y=0) and xy plane (z=z) ₀ ) Power density distribution of (a): (a) circular, (b) square, (c) 8-shaped, (d) rectangular. Points 101 to 104 in the xy plane identify the nanojet beam, whose shape and position are consistent with the predictions given in fig. 14 (these near field maps are calculated at arbitrarily chosen xy planes, defined with respect to the cavity basal plane).

In particular, fig. 15 (a) shows that an axially symmetric circular cavity produces a diverging cone beam, the cross-section of which in the vertical (xz) and horizontal (xy) planes is shown in top and bottom views, respectively, in fig. 15 (a). Notably, the cone beam is almost symmetrical (see near field pattern in the horizontal xy plane), which verifies polarization insensitive behavior of such components (or devices). The field strength enhancement observed in this configuration is a factor of 2, i.e., fie≡2a.u. (defined according to equation 2).

Fig. 15 (b) and 15 (c) show how the transition of the cavity cross section S from circular to rectangular and 8-shaped, respectively, results in the formation of a multi-beam near-field pattern with four (denoted 104) and two (denoted 103) nanojet beams. The beam forming effect involves the transition of the boundary segment from convex to planar and then concave, respectively. The light beams observed in fig. 15 (b) and 15 (c) have radiation angles similar to those of the cone beam generated by the cylinder (fig. 15 (a)). Meanwhile, the width of the light beam in azimuth is different. The larger the internal angle of the concave section of the cavity cross-section boundary S, the narrower the beam and the higher the field strength. Specifically, FIE et al for the two chambers shown in FIGS. 15 (b) (square) and 15 (c) (rectangle) are respectively 2.5a.u. and 2.8a.u..

Finally, fig. 15 (d) shows a broad leaf-shaped nanojet beam generated by a hollow rectangular cavity. This example demonstrates the possibility of forming a broad beam, which may be significant for certain applications requiring uniform illumination of a narrow shaped area.

The curvature of the boundary of the cavity is thus a tool for changing the shape, position and field strength enhancement of the nanojet beam.

More complex assemblies with symmetrical or asymmetrical cross-sections can be constructed using the same method, producing any number of the same or different nanojet beams, as shown in fig. 5.

However, the nano-jet focusing assembly (or device) previously described in fig. 4-15 has a light that is aligned with the nano-jet The finite field strength enhancement of the beam and some constraints associated with a fixed radiation angle, which need to be improved in order to make it possible to re-produce Nano-jet elements or assemblies (also known as nano-elements) now having the focusing function of their conventional analogs (e.g., refractive and diffractive micro-elements) A rice spray lens or device).

In one embodiment of the present disclosure, it is suggested to switch the configuration of the cavity in such a way that all nanojet beams originating from different segments of the cavity cross-sectional boundary recombine and contribute to the formation of a single high intensity nanojet beam that is located on and oriented along the symmetry axis of the cavity, i.e. not tilted compared to the incident plane wave.

To achieve this it is suggested to use a device comprising at least one layer of dielectric material, which at least partly comprises a first element (e.g. having the shape of a cylinder or cuboid as shown in fig. 16 (a)), which has a first refractive index value, which at least partly comprises a second element (e.g. having the shape of a cylinder, or other shape as shown in fig. 27), which has a second refractive index value, which is larger than the first refractive index value, and wherein the second element comprises at least one base surface defined with respect to the direction of arrival of the electromagnetic wave, and wherein the at least one base surface comprises at least two opposite edge line segments (see e.g. fig. 32), the shape (e.g. curvature) thereof and the associated base angle between the at least one base surface and the sides of the second element (in a perpendicular plane with respect to the at least one base surface) controlling the shape of the at least one focused beam (see e.g. fig. 32).

It should be noted that the intensity of the at least one focused light beam is defined by the lengths of the two pairs of corresponding edge line segments of the at least one base surface.

As schematically shown in fig. 16 (b), a desired effect can be achieved by exchanging refractive index values inside and outside the column. Additional advantages of the proposed ring-type structure include a natural solution to the problems associated with arranging the elements in space, which is a key disadvantage of microspheres, and its possible fabrication using standard optical materials and established planar micromachining techniques.

Fig. 17 (a) and (b) illustrate the general topology of a ring-shaped nanoinjector assembly. It has the form of a double-layer cylinder with an arbitrary cross section embedded in a homogeneous non-dispersive dielectric host medium. Hereafter we assume that the core of the cylinder has a refractive index n ₂ >n ₁ And it consists of a material having the same refractive index n as the main medium ₂ ＝n ₃ ＝n ₄ Is made of the material of (3).

For example, the host medium may have a refractive index similar to glass or plastic in the optical range (e.g., n ₂ =1.49) and the annular chamber is filled with vacuum or air, n ₁ ＝1。

In principle, the cylinder cross-section boundary S ₁ (core column) and S ₂ The (outer cylinder) may have any shape (symmetrical or asymmetrical). The influence of the size and shape of each boundary is studied later in the specification. In one embodiment of the present disclosure, the cylinder structure may be slanted and/or truncated and/or include a rounded top surface.

Hereafter we consider a cylinder structure with the vertical edges parallel to the z-axis and the top/bottom surfaces parallel to the xy-plane. However, as previously mentioned, some tapered and prismatic structures with arbitrary base angles may also be used. The variation of the base angle associated with different segments of the base edge line can be used to produce nanojet beams having different radiation angles. This option is not discussed here, but one skilled in the art can solve this problem in light of the teachings of the present disclosure.

In one embodiment thereof, the annular nano-jet element may be realized in the form of a double-layered cylinder. In the following analysis, we assume that its core is filled with the same material as the host medium (e.g., n ₂ ＝n ₃ =1.49), and outsideThe shell (cavity) is filled with vacuum or air (n) ₁ ＝1)。

Under the above assumption (i.e., double layer cylinder shape and pre-selected main dielectric material), the configuration of the annular nanojet member is controlled by three parameters, namely: its height along the z-axis (L _z ) And the radius (R ₁ R is as follows ₂ ＝R ₁ +w, where W is the width of the ring).

Focal length

In a first approximation, the focal length of the annular nano-jet element may be dependent on the core radius R ₁ And a nanojet beam radiation angle θ defined by equation (4) _B And (5) exporting. Given that the nanojet radiation angle remains constant for any combination of toroidal element height and radius, the focal length of the toroidal element can be estimated as:

F≈R ₁ /tan(θ _B ) (equation 5)

Where F is the distance from the bottom of the element to the point with the greatest field strength (fig. 18 (a)).

According to equation (5), embedded in the refractive index n ₂ ＝1.49(θ _TIR Hollow in main medium (n) ₁ In the case of =1) a ring-shaped nano-jet element, the focal length is estimated to be f≡2.25R ₁ 。

As can be seen from fig. 19, the actual value of the focal length (defined based on the position of the point with the maximum field intensity value) and the length of the nanojet beam may vary depending on the size and shape of the annular cavity. The family of four curves in FIG. 19 (a) shows a curve with a fixed ring size (R ₁ =370 nm, w=500 nm) but along the z-axis (defined by the parameter L _z Definition) the power density distribution of the different annular elements along the z-axis. For elements with a height less than (or greater than) the focal length, the observed hot spot is closer (or farther) than expected, for elements with a height close to the focal length L _z The best consistency is observed for the elements of F. Note that all curves in fig. 19 (a) are superimposed in such a manner that the element base positions are consistent for all configurations.

The increase in beam length observed in fig. 19 (a) is explained by the interaction between the nanojet and the fresnel focusing mechanism. The latter contribution becomes significant due to the insufficient cavity height, which prevents the formation of the nanojet beam (verified by a value of about twice the peak power density).

Incidence angle

In the case of oblique illumination, the nanojet beam angle is inclined in proportion to the inclination of the propagation direction of the incident wave (see fig. 20).

Width of ring, W

The width of the annular cavity may change the characteristics of the nanojet beam. In particular, it may affect the focal length and beam shape of the annular nanojet element.

Although the nanojet beam formation is associated with the base edge of the cavity, there is a finite size effective aperture responsible for its formation (see dashed line in fig. 16 (b)). The aperture extends from the side of the core cylinder to about half the wavelength in the respective medium on both sides. Thus, the minimum recommended width of the annular cavity is estimated to be W.ltoreq.1/2λ ₁ Wherein lambda is ₁ ＝λ ₀ /n ₁ 。

Too large a ring can also affect nanojet beam formation due to two phenomena associated with the overall size of the ring cavity, namely: (i) Internal reflection inside the annular cavity and (ii) fresnel focusing effects associated with diffracted waves originating from the top surface of the annular cavity. Empirical analysis suggests an upper limit of width, e.g., W.apprxeq.3λ ₁ . For larger rings, the contribution of the ring may become dominant, thereby masking the nano-jet phenomenon. However, if desired (e.g., for technical needs), the ring width can be quite arbitrarily enlarged without damaging the nano-jet phenomenon (fig. 21 (a)).

Furthermore, for each dimension (height and radius) of the core cylinder, the dimensions of the annular cavity can be optimized so as to:

increasing the field strength in the hot spot (figure 21),

-changing the length of the nanojet beam (fig. 22).

Note that the effect related to the height and width of the ring shape is narrower than the nano-jet beam phenomenon (fig. 23 and 24).

Field strength enhancement by combining nanojetting and fresnel focusing effects

Fig. 21 shows the effect of ring width on maximum field strength in hot spots of annular nano-jet elements. Here, in fig. 21 (a), it can be seen that the core has a fixed core size (L _z ＝740nm，R ₁ =370 nm) and the power density distribution of the variable loop width element along the z-axis. For convenience, the maximum values of power density observed for rings of different widths are plotted in fig. 21 (b) along with the location of the hot spot. The corresponding near field patterns are given in fig. 21 (c) - (f). As can be seen, a 40mW/m is achieved for a ring width W≡500nm (i.e. about one wavelength inside the cavity) ² Is a maximum power density of (c). According to equation (2), the corresponding field strength enhancement is fie≡20a.u., which is 10 times higher than the field strength enhancement observed for the hollow cylinder cavity 111 shown in fig. 7.

Length of nanojet beam

Fig. 22 shows the effect of ring width on the length of the nanojet beam. Here, the much lower field strength compared to the larger size element shown in fig. 21 verifies that the smaller height element prevents efficient generation of the nanojet beam. Therefore, the contribution of the fresnel focusing mechanism becomes equivalent to the nano-jet phenomenon. As a result, a longer beam is produced with two maxima along the z-axis.

Bandwidth of nano-jet and fresnel beam forming effect

The difference in physical mechanisms behind the nanojet and fresnel-type focusing mechanisms results in different bandwidths for these two phenomena.

The known fresnel focusing is based on interference of diffracted waves originating from the top surface of the annular cavity. Interference of waves generated by different segments of the ring top surface may result in the formation of multiple hot spots and beams corresponding to different diffraction orders. The direction of radiation of these beams and the location of the hot spot are therefore strongly dependent on the wavelength of the incident wave. Instead, the nanojet beam is generated independently at each segment of the cavity base edge line. Thus, the position and shape of the nanojet beam generated on the optical axis of the annular element due to the recombination of the nanojet beams generated by different segments of the cavity base edge line is less sensitive to the wavelength of the incident wave.

Fig. 23 and 24 show differences in dispersion behavior of two types of focusing mechanisms. In fig. 23, the element size corresponds to the case when the behavior thereof is defined by the superposition of the fresnel type and the nano-jet phenomenon (this configuration corresponds to the configuration studied in fig. 22 (e)). Thus, a significant change in the nanojet beam length was observed with respect to wavelength. In contrast, in fig. 24, the element size is selected so as to well maintain the beam shape for the entire wavelength range (this configuration corresponds to the configuration studied in fig. 21 (d)). This behavior verifies the dominant role of the nanojet effect in beam formation.

External ring shape, S ₂

The outer shape of the ring can be chosen quite arbitrarily.

As can be seen in fig. 25, the change in shape of the ring outer boundary of the ring (by S ₂ Definition) only slightly affects the nanojet beam. For example, the transition of the outer cylinder cross section from circular to rectangular results in only a small decrease (10%) in field intensity in the focus, the position of which remains almost unchanged for both configurations.

When its performance is defined by the interaction of fresnel-type and nano-jet phenomena (not shown), a greater impact can be expected for certain configurations of the ring-shaped element.

Core size, R ₁

The core size is a key parameter for the ring-shaped nano-jet element. This parameter determines the location of the hot spot along the z-axis and the peak field strength in the region of the nanojet beam.

The radius of the core cylinder defines the length and curvature of the edge line and thus the total effective aperture of the nano-jet element. The longer the edge, the more power is captured and directed to the nanojet beam, thereby increasing the field strength in the focal point.

Having the same material (n) in the core, substrate and superstrate ₂ ＝n ₃ ＝n ₄ Symbol see fig. 17), a linear increase in field strength with respect to the core cylinder radius is observed (fig. 26). In case the ring element structure comprises a stack of layers of different materials, internal reflection inside the core may occur and alter the nano-meterJet beam forming conditions. The larger the index ratio, the larger the core size and the greater the possible impact of internal reflection (i.e., the greater the number of supportable resonant modes inside the core barrel and the higher the quality factor of certain modes).

Optimal combination of element height and radius with influence of main dielectric material

The optimum ratio between core height and radius due to the nanojet focusing effect and the estimated FIE is a function of the refractive index ratio between the element core and cavity material. For embedding in a refractive index n ₂ In an unbounded main medium =1.49 with a hollow ring (n ₁ Full wave analysis of the annular nanojet element of =1) reveals that for L _z /R ₁ And (c) 2 achieves maximum field strength (fig. 26 (a)). The corresponding field strength enhancement is estimated as FIE-18R ₁ /λ ₁ [a.u.](at least for 1/2)<R ₁ /λ ₂ <2 is active). At n ₁ In the case of =2.0, the optimal ratio is defined as L _z /R ₁ =1.4 (fig. 26 (b)). The corresponding field strength enhancement is estimated as FIE-16R ₁ /λ ₁ [a.u.](at least for 1/2)<R ₁ /λ ₂ <3 is valid).

Core shape, S ₁

The shape of the core cylinder can be quite arbitrarily chosen and optimized to provide the desired shape and size of the nanojet beam (fig. 27 and 28).

Modification of the core shape of the annular nanojet element enables modification of the partial contribution of the nanojet beam associated with different segments of the core-based edge line. Fig. 27 illustrates some exemplary embodiments of ring-shaped nano-jet elements having cores of different shapes. The beam that contributes to the formation of the central nanojet beam is schematically shown by a dashed line. Fig. 28-30 show the corresponding power density profile for each configuration. As can be seen in fig. 28 (a) and 28 (b), the transition of the core cylinder cross-section from circular to square has only a slight (about 10%) effect on the maximum of the power density in the hot spot (best seen in fig. 29), while the hot spot location and beam symmetry are well preserved for both circular and square configurations (fig. 30 (a) and 30 (b)). As can be seen in fig. 28 (c) and 28 (d), the conversion of a circular core into more complex 8-type and bar-type shapes results in the formation of an asymmetric beam, the shape of which reproduces the shape of the core. In addition to the nanojet beam width and length, the transition of the core shape also affects the maximum power density of the hot spot of the nanojet beam (fig. 29). As expected, the maximum value was observed for a round core (due to its symmetry) and the minimum value was observed for an element with a rectangular core in strip form. Fig. 30 shows a cross-sectional view of the beam of each configuration.

Fig. 31 presents a schematic view of a usage scenario of a nano-jet focusing assembly (or a device for forming at least one focused light beam in a near zone) according to one embodiment of the present disclosure.

In such an embodiment, the emitting element (as an illumination unit) labeled 280 may be any electromagnetic radiation source (e.g., light, even UV light) located in the near or far region. The electromagnetic waves generated by the emitting element 280 may propagate via free space or through an optical projection unit comprising a set of lenses and/or mirrors and/or other optical components to a nano-jet focusing element labeled 281 (either as part of a device for forming at least one focused light beam in the near zone or as such a device for forming at least one focused light beam in the near zone).

The nanojet focusing element 281 can generate a nanojet beam in response to receipt of an electromagnetic wave, which can be used to create a geometric pattern on a photoresist layer element. The photoresist layer elements should be located a distance D R from the nanojet focusing element 281 _max And (3) inner part. The optimal distance depends on the focal length and the nanojet beam shape. It can vary from 0 to several wavelengths. R is R _max The values of (2) will be defined in accordance with specifications of system functions that may be formulated, for example, in accordance with acceptable field strength enhancements. R is R _max Is estimated to be 3 to 10 wavelengths.

In one embodiment of the present disclosure, nanojet focusing element 281 is a photomask for a lithography process.

It should be noted that in one embodiment of the present disclosure, the nano-jet focusing element 281 comprises a multi-layer structure having "(cavity(s)" on one or both surfaces of the sealing substrate. In some configurations, these structures may be directly attached to the receiving and/or transmitting elements.

In one embodiment of the present disclosure, the emitting element 280 is a laser.

It should be noted that in one exemplary embodiment, the aforementioned annular nano-jet element may be manufactured in the form of a multi-layer structure comprising three layers, namely: (i) a glass plate, (ii) a film with perforated apertures made of an optically transparent photoresist or phase change material, and (iii) another glass plate (e.g., another glass film).

It should be noted that a photomask according to one embodiment of the present disclosure may be fabricated, for example, by direct laser beam writing methods, replication, or molding. The manufacturing process of the photomask is given as an example only in order to highlight the manufacturing feasibility of the device according to the present disclosure using the established micro-manufacturing method. However, there may be some other manufacturing method, or more suitable for mass production.

Fig. 32 illustrates two different views of a second element according to one embodiment of the present disclosure.

These views present at least three parameters associated with the second element that can control the shape and orientation of the focused beam: the length and curvature of the edge line segments associated with the base surface, and the value of the base angle associated with the opposite edge line segment.

Fig. 33 presents a 3D view of a second element, representing two pairs of opposing edge line segments that facilitate the formation of two independent nanojet beams, in accordance with an embodiment of the present disclosure. At L ₁ ≈L ₂ The two nanojet beams may be recombined into a single beam having a more complex shape (see, e.g., fig. 28 (c)). At L ₁ <<L ₂ The nanojet beam (2) may occur at a greater distance from the top surface of the element and have a much lower field strength value than the nanojet beam (1). For L, for example ₂ >This may occur with 5λ, where λ is @ in the host mediumI.e., intracavity).

Fig. 34 presents an intersection of a portion of a device according to the present disclosure by a plane parallel to the propagation of an incident electromagnetic wave (more precisely, normal incident electromagnetic wave with respect to the bottom of the dielectric layer).

Fig. 35 (a) - (d) present different resulting crossover points for a portion of the device according to the present disclosure by being parallel to the plane of propagation of the incident electromagnetic wave (more precisely, normal incident electromagnetic wave with respect to the bottom of the dielectric layer).

It should be noted that the nanojet beams generated due to the interference of the two parts of the wave fronts of the incident wave propagating through the base of the first and second elements recombine together inside the second element, producing a focused nanojet beam. In the case of normal incidence of a plane wave, for an element of equal value having a symmetrical cross-section and the previously mentioned base angle associated with the opposite base edge line segment, a symmetrical nanojet beam is produced on the optical axis of the element having an orientation along that axis. It should be noted that in the case of oblique incidence of plane waves, the light beam is proportionally tilted.

The shape, position and radiation angle of the nanojet beam(s) can be controlled by one skilled in the art by varying the shape and size of the first and second elements, and in particular by varying the shape of the base edge line and the associated base angle. Thus, the focusing and beam forming characteristics of the nano-jet focusing apparatus can be controlled according to the selected parameters.

Fig. 36 presents a schematic view of a nanojet beam generated by a device (or ring-shaped nanojet element) illuminated by a plane wave according to one embodiment of the disclosure: (a) Incident from below along the z-axis, (b) incident from the left side along the x-axis. Arrows from the first element indicate the nanojet beam. Fig. 36 (c) presents a power density distribution in the xz plane when the device according to an embodiment of the present disclosure, i.e. comprising a ring structure, is illuminated from the left side (along the x-axis).

It should be noted that in case of plane waves incident from the left side, at least one base surface of the aforementioned second element corresponds to a side surface of the cylinder, in common sense at least two edge line segments are part of the top and bottom edge lines of the cylinder. However, the person skilled in the art will understand this variation of common sense.

Fig. 37 (a) - (c) present some examples of NJ microstructure architecture (from above): (a) a ring shape, (b) a curved strip, (c) a grid, (d) a regular or periodic groove.

Fig. 38 (a) shows the photoresist layer (n) ₂ Glass plate on top of =1.7) (n _l =1.5 nm), fig. 38 (b) shows the normalized field intensity in the YZ plane when irradiated with plane waves (λ=365 nm) from above, fig. 38 (c) shows the normalized field intensity distribution along the X and Y axes at z= -100nm, and fig. 38 (d) shows the normalized field intensity distribution along the Z axis. Fig. 39 presents (a) the normalized field intensity in the XZ plane of an annular NJ microlens illuminated by a plane wave (λ=365 nm) having an angle of incidence of 20 ° defined with respect to the vertical axis, and (b) the normalized field intensity distribution along the X axis at y=0 nm, z= -100nm for plane waves of two different angles of incidence (0 ° and 20 °). The parameters of the structure are the same as in fig. 38.

Thus, a photomask according to the present technology enables the fabrication of complex patterns on a photoresist layer. Indeed, as explained in the aforementioned article "photon jetting and its application in nanophotonics" by the author of Hooman Mohseni, the orientation of the photoresist layer and mask according to the present disclosure may also be changed in the same manner as described in detail in fig. 1 (a) of the mentioned article. Due to the flexibility (in terms of the orientation of the resulting nanojet beam) caused by the nanojet focusing element, the photomask according to the present technology allows more complex patterns to be obtained on the photoresist layer compared to a photomask comprising only nano (or micro) spheres.

FIG. 40 presents an example of a lithographic apparatus according to an embodiment of the present disclosure.

Such lithographic apparatus, denoted 3900, comprises a computing unit (e.g. a CPU, "central processing unit") denoted 3901, and one or more memory units (e.g. a RAM ("random access memory") block, which may temporarily store intermediate results during execution of computer program instructions, or a ROM block storing a computer program or the like, or an EEPROM ("electrically erasable programmable read only memory") block or flash memory block) denoted 3902. The computer program is constituted by instructions executable by a computing unit. Such a lithographic apparatus 3900 may also include a special purpose unit, denoted 3903, which constitutes an input-output interface to allow the apparatus 3900 to communicate with other apparatuses. In particular, the special unit 3903 may be connected with an antenna (to communicate without contact) or with a serial port (to communicate "contact"). Units 3901, 3902, and 3903 may exchange data together, for example, over a bus.

Furthermore, the lithographic apparatus 3900 includes an illumination unit (which may be a laser or any unit that may generate light in a lithographic environment) labeled 3904 that may be guided by the computing unit 3901. In one embodiment of the present disclosure, the lithographic apparatus may comprise an optical projection unit, denoted 3905, for directing light emitted by the illumination unit 3904 to a photomask, denoted 3906. Photomask 3906 includes nanojet generating elements according to the present disclosure for generating geometric patterns/structures on a photoresist layer labeled 3907.

Fig. 41 shows a specific embodiment of the present disclosure, according to which the focusing assembly is based on a hollow cuboid 2 x 2 array embedded in a main medium. Fig. 41a shows the topology of such a component, while fig. 41b provides a plane wave of unit amplitude (n ₁ ＝1.49，L _x ＝L _y ＝L _z ＝2λ ₁ ，S＝0.5λ ₁ ) Simulation results of time-averaged power distribution at the time of irradiation.

The assembly (or photomask) of FIG. 41a includes a refractive index n embedded therein ₁ >n ₂ Four hollow rectangular parallelepiped (n) ₂ =1) 140. For example, this may be glass, plastic (e.g., PMMA), or polymer (e.g., PDMS (polydimethylsiloxane)).

Embedded in refractive index n ₁ Hollow in uniform dielectric 112 of=1.49 (n ₂ =1) on-axis generation of 2×2 array of cuboids 140, wherein refractive index n ₁ =1.49 is a typical value for glass and plastic in the optical range. Analysis shows that by optimizing the size, shape and relative position of the cuboid with respect to the refractive index of the host medium and the wavelength of the incident plane wave, a light having a wavelength of λ/2n can be generated ₁ A full width half maximum (FWHP) and a factor of at least 5.

Fig. 42 shows an alternative embodiment of a photomask in which a hollow rectangular cuboid 140 is replaced by a hollow cylinder 141 oriented along the plane wave propagation direction. Like fig. 41, fig. 42a shows the topology of such a component, while fig. 42b provides a unit amplitude plane wave (n ₁ ＝1.49，L _z ＝2λ ₁ ，R＝λ ₁ ，S＝0.5λ ₁ ) Simulation results of time-averaged power distribution at the time of irradiation.

Fig. 43 shows yet another embodiment, in which a 2 x 2 array of hollow cylinders 141 is formed at the boundary of dielectric 112 and free space, for example, on the surface of a glass or plastic plate. Such an assembly (included in a photomask) produces a nanojet beam in free space near the surface of plate 112 when illuminated by a plane wave from the media side. This embodiment is advantageous for applications requiring an air gap between the focusing assembly and the object under test (typical scenarios of optical data storage, microscopy, spectroscopy and metrology systems).

As in fig. 42, fig. 43a shows the topology of such a component based on a 2 x 2 array of hollow cylinders created at the interface of dielectric and free space, while fig. 43b provides the effect of the signal when the component is formed by a plane wave of unity amplitude (n ₁ ＝1.49，L _z ＝2λ ₁ ，R＝λ ₁ ，S＝0.5λ ₁ ) Simulation results of time-averaged power distribution at the time of irradiation.

FIG. 44 provides two additional exemplary embodiments of single-period (FIG. 44 a) and dual-period (FIG. 44 b) arrays based on hollow cylinders 141 embedded in a host medium 112 and included in a photomask according to one embodiment of the present disclosure. In both embodiments, the hollow cylinders form a plurality of regularly spaced sub-arrays of 2 x 2 closely positioned scatterers, which function similarly to the assembly shown in fig. 42. Note that in the case of fig. 44b, each hollow cylinder 141 simultaneously contributes to the formation of four nanojets, labeled 180.

Claims

1. A lithographic apparatus for generating structures on a photoresist substrate, the lithographic apparatus comprising:

an illumination unit;

a photomask, wherein the photomask generates a nano-jet near field pattern that directly modifies the photoresist substrate to obtain the structure, wherein the photomask comprises at least one layer of dielectric material; and

A medium having a refractive index lower than that of the dielectric material, wherein a surface of the at least one dielectric material layer has at least one abrupt level change forming a step, and wherein at least a base and a side of the surface with respect to the step and a direction of electromagnetic waves from the illumination unit are in contact with the medium;

wherein the nano-jet near field pattern is constructive interference of electromagnetic waves from the base and sides of the surface.

2. The lithographic apparatus of claim 1, wherein the step is formed by an edge of at least one cavity made in the at least one layer of dielectric material, and the cavity is at least partially filled with the medium.

3. The lithographic apparatus of claim 2, wherein the at least one cavity is a via in the at least one layer of dielectric material.

4. A lithographic apparatus according to any of claims 2 to 3, wherein the at least one cavity belongs to at least one set of at least two cavities.

5. A lithographic apparatus according to any of claims 2 to 3, wherein the at least one chamber target is cylindrical or conical.

6. The lithographic apparatus of claim 1, wherein the step is formed by an edge of at least one recess made in the at least one layer of dielectric material, and the recess is at least partially filled with the medium.

7. A lithographic apparatus according to any one of claims 1 to 3, wherein the height of the step, hvarget, is such thatWherein lambda is ₁ Is the wavelength of the electromagnetic wave in the dielectric material.

8. A lithographic apparatus according to any of claims 1 to 3, further comprising forming at least one layer of the substrate (110) adjacent to the layer of dielectric material.

9. A lithographic apparatus according to any one of claims 1 to 3, wherein the dielectric material is selected from the group consisting of: glass; a polymeric material.

10. A lithographic apparatus according to any of claims 1 to 3, further comprising an optical projection unit for directing light from the illumination unit.

11. The lithographic apparatus of claim 10, wherein the optical projection unit comprises a set of lenses and/or mirrors.

12. A lithographic apparatus according to any one of claims 1 to 3, wherein the dielectric material is an optically transparent dielectric material.

13. A lithographic apparatus according to any one of claims 1 to 3, wherein the medium is a solid or a liquid or a gas.